1. Field of the Invention
The present invention relates to a beamforming-based wireless mobile communication system. More particularly, the present invention relates to a communication method and apparatus using analog and digital hybrid beamforming.
2. Description of the Related Art
The development trend of wireless communication systems is toward higher data rates to satisfy ever increasing demands for wireless data traffic. For example, wireless communication systems are being developed toward increased spectral efficiency based on communication schemes such as Orthogonal Frequency Division Multiple Access (OFDMA), Multiple Input Multiple Output (MIMO), and the like in order to increase data rates.
As demands for traffic have accelerated due to increased demands for smartphones and tablet Personal Computers (PCs) and the resulting rapid growth of applications requiring a large amount of traffic, it is difficult to satisfy the soaring demands for wireless data simply by increasing spectral efficiency.
To avert the problem, recent interest has focused on a millimeter-wave wireless communication system. When wireless communication is provided in a millimeter-wave frequency band, propagation loss, such as path loss and reflection loss, is increased in view of the spectral nature of the millimeter-wave frequency band and the resulting shortened propagation distance reduces service coverage. Therefore, the millimeter-wave wireless communication system may expand service coverage by mitigating the path loss of waves using beamforming and thus increasing the propagation distance of the waves.
The two types of beamforming schemes are digital beamforming (or Transmit (Tx) pre-Inverse Fast Fourier Transform (pre-IFFT) beamforming/Receive (Rx) post-Fast Fourier Transform (post-FFT) beamforming) and analog beamforming (or Tx post-IFFT beamforming/Rx pre-FFT beamforming). Digital beamforming uses a plurality of Radio Frequency (RF) paths based on Multiple Input Multiple Output (MIMO) and a digital precoder or codebook in the digital domain, and analog beamforming uses a plurality of analog/RF devices (e.g., a phase shifter, a Power Amplifier (PA), and a Variable Gain Amplifier (VGA)) and an antenna configuration. While digital beamforming requires an expensive Digital to Analog Converter (DAC) or Analog to Digital Converter (ADC) and increases implementation complexity in order to increase a beamforming gain, analog beamforming has limitations in terms of efficient use of frequency resources or maximization of beamforming performance.
Since a wavelength is shortened in a millimeter-wave band, analog beamforming using an antenna array with a number of antenna elements arranged in a small space, such as a Uniform Linear Array (ULA) or a Uniform Planar Array (UPA), is suitable. However, the analog beamforming has limitations in its effectiveness in terms of efficient use of resources, the increase of user or system throughput through MIMO schemes such as Single User MIMO (SU-MIMO), Multiple User MIMO (MU-MIMO), or spatial multiplexing, and the increase of Signal to Noise Ratio (SNR) or reliability through diversity or additional digital beamforming, as described before.
Accordingly, there exists a need for supporting a hybrid beamforming which is a combination of analog beamforming and digital beamforming, for efficient MIMO/beamforming.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.